Over a hundred thousand laboratories worldwide analyze hundreds of thousands of samples everyday to detect various metals, minerals and other chemicals within the samples. The types of samples are diverse and include wastewater, sludge, sediments, soils, rocks, foods, pharmaceuticals, industrial and manufactured products, animal and plant tissue, plastics, oils, steel, greases, coal, cements, paint chips, etc. The laboratories for testing these samples are also diverse and include environmental, mineral (geotechnical), quality control, industrial, food, research, governmental, regulatory, university, commercial testing laboratories, etc. Furthermore, these laboratories can either be high volume, and may analyze thousands of samples per day, such as commercial testing laboratories. The laboratories may also be low volume, such as small industrial quality control laboratories, and may analyze a few samples per day. One common trait among these laboratories is that that each sample undergoes sample preparation, and specifically digestion or other types of dissolution, before the laboratory can analyze the sample.
The dissolution process converts the sample into a liquid medium so that standard analytical instruments can analyze the sample. When dealing with samples from environmental, geological and other areas, the samples are often solid or semi-solid samples, and these samples are not always submitted to the laboratory in a clear liquid form. Accordingly, the solid and semi-solid samples need to undergo ‘sample preparation’, such as ‘sample dissolution’, in order to convert the sample into a clear solution for subsequent chemical analysis using standard analytical instruments. For certification purposes, the sample preparation process must be quantitative and repeatable, and sample integrity must be maintained during each stages of the sample preparation process in order to be suitable for later analysis.
There are different types of sample preparation procedures that are recognized and approved worldwide. The following are a few examples of these sample preparation procedures.
Acid digestion is a procedure in which a sample is placed in a beaker on a hot plate and an acid mixture is added in order to dissolve the sample. This procedure uses large volumes of volatile acids, which evaporate and escape into the environment. To reduce harmful gaseous emissions, the acid vapours are often vented into large expensive ($15,000 to $50,000) fume hoods with exhaust scrubbers. Unfortunately, the scrubbers produce large volumes of acidified wastewater, which still represents an environmental disposal issue. Acid digestion also has a number of other problems. In particular, acid digestion can take many hours, requires continuous monitoring, and is manual and labour intensive. Acid digestion is also prone to element loss and contamination problems and generally has poor precision. It is also difficult to automate and computerize the acid digestion process. The handling of hot acid also represents a safety issue.
Acid digestion can also be performed using a hot block, which is a large heated block having a number of openings for receiving test tubes that contain a sample and acid. The procedure is similar to acid digestion in a beaker, but the hot block allows automation, at least in a rudimentary fashion, using a controller. Furthermore, these hot blocks can be connected to, and controlled by, an auto-prep workstation. However, acid digestion in a hot block still suffers from the other disadvantages noted above with respect to acid digestion in a beaker.
Computer controlled microwave acid digestion is another sample preparation processes whereby a sample and acid are placed into a closed vessel and heated by microwave radiation. Volatile elements are contained within the closed vessel, which offers better control over exhaust fumes and reduces environment impact. Microwave acid digestion also uses less acid because the acid is contained within the vessel. However, microwave acid digestion still suffers from a number of problems. While microwave acid digestion can be automated and computer controlled, it is hard to automate in an auto-prep workstation and does not offer high production rates. Furthermore, while the process might offer better digestion times for samples that are otherwise difficult to digest, sample digestion can actually be slower for some samples in comparison to wet digestion in a beaker or hot block. Safety is also an issue because there are high-pressure acid vapours within the closed vessels. Furthermore, the closed vessels are expensive to make, hard to clean, and difficult to work with. Sample sizes are often limited to 0.5-1.0 grams, which tends to be smaller than the sample sizes laboratories prefer to use. Another draw back is that the digestion vessel is often made from Teflon™, which means the maximum digestion temperature cannot exceed 230° C., otherwise the Teflon lining might distort or deteriorate and can contaminate the sample. Batch capacity is also limited, making it unattractive for high volume throughput laboratories. While microwave acid digestion might be appropriate for low volume laboratories that need to digest difficult samples without worrying about productivity and cost per test issues, the process is not suitable for high volume laboratories that need to worry about productivity and costs while analyzing a diverse range of samples
Microwave ashing is a computer-controlled process whereby a sample contained within a vessel is heated in the presence of oxygen in order to convert the sample to ash. After converting the sample to ash, the sample can be dissolved more readily in a solution, such as an acid mixture. Like microwave digestion, microwave ashing is a specialty digestion technology that offers faster digestion times for normally hard to digest samples. While microwave ashing is computer controlled, it is difficult to automate in an auto-prep workstation. As such, microwave ashing tends to be appropriate for low volume laboratories, but it is not a production tool and is generally unsuitable for higher volume laboratories. Furthermore, with microwave ashing tends to have a greater risk of sample contamination and of losing volatile elements in comparison to microwave acid digestion.
It is apparent that conventional procedures for sample preparation and dissolution have numerous disadvantages. While each procedure described above might be appropriate for some samples, they might not be appropriate for others. In particular, many of these conventional procedures are not designed with productivity (cost per sample) in mind and are often viewed as manual methods because they require extensive technician intervention and labour. Furthermore, it can take many hours to dissolve or digest samples, and many procedures can only dissolve or digest a small number of samples at a time. This represents a growing problem within the industry, and particularly for the commercial analytical testing industry because regulators, governments and commercial pressures are promoting automation and computerization of laboratories for productivity, traceability, and trackability.
For high volume commercial testing laboratories, which need to automate the most for productivity, tracing, and tracking issues, there is no single sample preparation procedure currently available that overcomes the problems with the conventional procedures. As a result, commercial laboratories often utilize multiple independent sample preparation units, including one or more of the above conventional procedures. This is undesirable because having multiple sample preparation makes it more difficult to automate the laboratory and it is hard to achieve high productivity. As such, sample preparation remains an unsafe, environmentally unfriendly, and inefficient work environment in many analytical laboratories.
Furthermore, some of these conventional procedures are slow, uneconomical, and environmentally unfriendly, such as wet acid digestion. As such, these procedures often involve costly remedial steps that attempt to minimize or eliminate the otherwise harmful environmental impact. Due to these costly remedial steps, and the currently competitive market for sample analysis, many analytical laboratories are avoiding sample preparation processes that are not environmentally friendly.
It is therefore apparent that conventional sample preparation procedures can be tedious, labour intensive, time consuming and/or environmentally unfriendly (for example: acid fumes getting into the environment). However, these conventional procedures are still used today because there is not a better procedure that meets or exceeds the performance of these old conventional procedures.
In view of the above, there is an urgent need for apparatus, systems and methods for preparing samples for chemical analysis that overcome one or more of the problems identified above.